A liquid crystal display device is configured with a pair of substrates that are disposed to be opposed to each other with a liquid crystal layer sandwiched between the substrates. Over a surface, facing toward the liquid crystal layer, of a first substrate of the pair of substrates, gate lines extending in an X direction and evenly spaced and arranged in a Y direction and drain lines extending in the Y direction and evenly spaced and arranged in the X direction are formed. A rectangular area surrounded by these lines is defined as a pixel area. A display region is formed by a collection of all these pixels.
Each pixel includes a thin-film transistor that is turned on by a scan signal from a gate line and a pixel electrode to which a visual signal is supplied from a drain line via a source electrode of the turned on thin-film transistor.
In such liquid crystal display device, an inorganic insulation film is formed over the surface of each thin-film transistor, thus covering the surface, facing toward the liquid crystal layer, of the first substrate including the thin-film transistors. An organic insulation film serving as a planarizing film is formed over this inorganic insulation film surface toward the liquid crystal layer. Over the organic insulation film surface toward the liquid crystal layer, pixel electrodes are disposed and a pad extending from the source electrode of a thin-film transistor and a part of a pixel electrode are formed in an overlap location. In this overlap region, a contact hole is formed which penetrates through the organic and inorganic insulation films and extends to the pad for electrical connection between the pixel electrode and the source electrode.
Meanwhile, as the scope of application to liquid crystal display devices has expanded lately, even higher image quality and definition are demanded. To realize higher definition, it is needed to increase the aperture ratio of a liquid crystal display panel, in other words, the aperture ratio of each pixel. As a liquid crystal display device with an increased aperture ratio, it is conceivable to form a film that forms the contact hole for electrical connection between the pad and the pixel electrode with a large taper angle, reduce the area occupied by the contact hole in a pixel area, and increase the aperture ratio.
A liquid crystal display device in which the contact hole with a large taper angle is formed is, for example, a liquid crystal display device described in Japanese Published Unexamined Patent Application No. 2008-64954. According to a technique described in Japanese Published Unexamined Patent Application No. 2008-64954, a pad is formed in a layer overlying an interlayer dielectric film and a contact hole with a taper angle of 60 degrees is formed in an organic insulation film which is formed to cover the pad. By this configuration, a pixel electrode that is formed on the surface of the organic insulation film and the pad are electrically connected.
However, it is known that, when an organic insulation film having a contact hole is formed, particularly when an organic insulation film having a contact hole is formed with a negative-type organic material, the forming process requires exposure time that is two or three times as much as the exposure time forming other inorganic insulation films. Especially, to form an organic insulation film having a contact hole with a taper angle of 60 degrees, as described in Japanese Published Unexamined Patent Application No. 2008-64954, a still larger amount of exposure is required. Therefore, it is feared that throughput of liquid crystal display device production may be significantly decreased due to increased time required for production. In addition, use of some material (resist material) of organic insulation film makes it impossible to form a contact hole with a taper angle of more than 60 degrees.